Groups elmenets of an async interable source according to a specified keySelector function and creates a map of each group key to the elements in that group. Key values are compared using the === operator.

import { groupBy } from "./unique.ts";

interface IdName { id: number; name: string; }
async function* gen(): AsyncIterableIterator<IdName> {
  yield { id: 1, name: "foo" };
  yield { id: 2, name: "bar" };
  yield { id: 3, name: "bar" };
  yield { id: 4, name: "foo" };
}

const map = await groupBy<string, IdName>(gen(), o => o.name);
console.log(map);

The above example will print the following:

Map {
 "foo" => [ { id: 1, name: "foo" }, { id: 4, name: "foo" } ],
 "bar" => [ { id: 2, name: "bar" }, { id: 3, name: "bar" } ]
}